Oxidation op petroleum cyclohexane



June 19, 1951 c. H. HAMBLE-r ETAL 2,557,281

OXIDATION oF psmomuu cYcLoxmxAnE Filed April 17, 1948 INI/mw @LEMA-NTM 57' mpim/Luv ##15 of HYnRbcARaoN (sulfur containing) Patented June 19,1951

OXIDATION OF PETROLEUM CYCLOHEXANE Clement H. Hamblet and Franklin S. Chance, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application April 17, 1948, Serial No. 21,583

Claims.

This invention relates to the oxidation of liquid hydrocarbons with gaseous oxygen and more particularly to oxidation of cyclohexane-containing petroleum fractions.

It is now well known that oxidation of cyclohexane to partial oxidation products constitutes an important step in the manufacture of nylon intermediates, e. g. adipic acid, etc. The process of oxidizing cyclohexane in the liquid phase to cyclohexanol and cyclohexanone at low conversions and high yields was disclosed several years ago (cf. the Loder patents U. S. 2,223,493, 2,223,494 and 2,321,551). In general, this process,.when carried out on a laboratory scale, gave cyclohexanol-cyclohexanone yields of about 85 to 95% when the percentage of cyclohexane molecules oxidized was less than 5%. When the percentage of cyclohexane molecules oxidized was from about 5% to about 12%. the yield of cyclohexanol-cyclohexanone was about 65% to 85%. In plant scale operations, the yields of cyclohexanol and cyclohexanone have been considerably lower, and, in fact, it has been extremely difficult to attain cyclohexanol-cyclchexanone yields exceeding about 70% at 'conversions of 5% to 12%, in large scale plant operations. In this previously known process cyclohexane from any source could be employed, but generally cyclohexane obtained by hydrogenation of benzene was 'preferably used. Since, in this previously known process for the oxidation of cyclohexane to cyclohexanol, cyclohexanone and other products, it was necessary to recycle relatively large quantities of cyclohexane, losses resulting from purging undesirable constituents from the oxidation mixture necessitated the use of extremely pure cyclohexane, and even then affected the cost of producing nylon intermediates via cyclohexanol and cyclohexanone adversely, in a very substantial way.

A primary object of the invention is to provide a practical process for oxidizing petroleum cyclohexane fraction to intermediates which on further oxidation in a separate step, yield adipic acid in higher yields than have been realizable heretofore. A further object is to provide a process for oxidizing sulfur-containing petroleum cyclohexane crudes, which also contain aromatic hydrocarbons, and separating the aromatic hydrocarbons from the reaction mixture in sulfurfree form, so that they can readily be hydrogenated and returned to the oxidation mixture. A further object is to provide an improved cyclohexane oxidation process, whereby cyclohexanol and cyclohexanone (together with other valuable products. many of which yield adipic acid on further oxidation) can be obtained in high yield without the accumulation of undesirable ingredients in the reaction mixture. Another object of the invention is to provide an improved process for oxidizing petroleum cyclohexane crudes to cyclohexanol and cyclohexanone. A more specific object is to provide a process for oxidizing sulfur-containing petroleum cyclohexane crudes to adipic acid intermediates, while recyclingunreacted hydrocarbon and at the same time avoiding the accumulation oi' aromatic compounds, or products derived therefrom, in the oxidation mixture, and also recovering aromatic hydrocarbon from the reaction mixture in sulfur-freeA form. Other objects of the invention will appear hereinafter In the manufacture of adipic acid from cyclohexane it was formerly considered that best results could be obtained by oxidizing cyclohexane to cyclohexanol and cyclohexanone in high yield and low conversion (U. S. 2,223,494) followed by separation of these intermediates. thereafter converting the cyclohexanol to cyclohexanone, and oxidizing the latter to adipic acid with air in a separate operation. More recently it has been disclosed (U. S. 2,439,515) that far better overall results are obtained by oxidizing mixed primary oxidation products (obtained from cyclohexane) to adipic acid by means of a nitric acid oxidation process. This made the obtaining of maximum yields of cyclohexanol and cyclohexanone, (the yield of cyclohexanol-cyclohexanone is maximum at low conversions) less desirable an objective than thesobtaining of maximum yields of the mixed oxidation product which in the subsequent steps would` bconvertible to adipic acid. The present invention is therefore directed to a process for oxidizing petroleum cyclohexane crudes to cyclohexanol and cyclohexanone, and to other products which are of value as adipic acid intermediates (as well as to still other products which are of very great value. as disclosed hereinafter); a purpose of the invention is to accomplish this desirable result by means of a process which is suitable for large scale production, i. e. which does not necessitate conversions below about and which can be operated for an unlimited period of time without any need for purging valuable ingredients of the mixture which would otherwise accumulate and preclude continued operation of the process.

This invention is based in part upon the discovery that the sulfur compounds which are present in petroleum cyclohexane crudes are destroyed when the said crude is oxidized as described hereinafter.- The inventionis also based in part; upon the discovery that'the benzene which is present in petroleum cyclohexane crudes (which generally contain at least a few tenths of a percent of benzene) is very resistant to oxidation under the conditions which are needed for the oxidation of cyclohexane to cyclohexanol and cyclohexanone in high yields. This benzene accumulates in the reactionv mixture and in the 'course of time, unless this accumulated benzene is removed, it causes substantial losses in the rate of cyclohexanol-cyclohexanone production per unit volume of reaction space. `The other hydrocarbons normally present in petroleum cyclohexane crudes oxidize at such a rate, and in such a manner, that the said hydrocarbons do not accumulatein the reaction mixture, and the oxygenated products obtained therefrom can readily be separated from those simultaneously formed from cyclohexane. Accordingly, it has been discovered that if Ibenzene is periodically removed from the recovered and recycled hydrocarbon, the oxidation of petroleum cyclohexane crudes can be continued for indeterminately long periods of time with recycling of the recovered cyclohexane fraction without any decrease whatever in the yield or rate of production of the desired oxidation products. It is highly significant that the benzene which is thus removed is free of sulfur, even though organic sulfur compounds were present in the petroleum cyclohexane. crude initially charged. The invention is also based in part upon still another discovery, namely the observation that if certain hydrocarbons, including aliphatic hydrocarbons, having from 6 to '1 carbon atoms per -molecule (e. g., .dimethyl pentane, methyl cyclopentane and/or n-hexane) are present in the petroleum cyclohexane crude containing a relatively small quantity of benzene, and the oxidation of the petroleum cyclohexane crude is carried out in the liquid phase at a temperature between '15 and 200 C, under 50 to 500 pounds per square inch pressurewith the oxygen absorption limited so that about'5% to 30% preferably about 12% to 25% of the hydrocarbonpresent is oxidized, a liquid reaction product is obtained which on distillation yields an azeotropic fraction which is rich in benzene-and which contains these hydrocarbons of the4 reaction mixture. Cyclohexane may be present in this fraction, but is not necessarily an azotropic ingredient. This discovery makes it possible to purge benzene from the oxidation mixture periodically without excessive loss of cyclohexane or other valuable substances. The said aliphatic hydrocarbons play a-very significant role in. the preferred embodiment of -the invention,` by facilitating the removal of benzene which makes possible the operation of the `continuous process for indefinitely long periods of time without purging the more valuable ingredients of the reaction mixture.

It is essential inthe practice of the invention to. provide a means for removal of water from the reaction zone, since water, which is produced as one of the products of the oxidation reaction, affects the oxidation reaction adversely. If the water is not removed it acts as an inhibitor by withdrawing from the oxidation zone substances which initiate and accelerate the desired reaction. A suitable method for removal of water is to have the oxidizer equipped with a reflux condenser and a device'for withdrawal of water layer from the condensate produced by the said condenser.

Thus, the present invention provides a process for manufacturing partial oxidation products of cyclohexane, notably cyclohexanol and cyclohexanone, by reacting a petroleum cyclohexane crude in the liquid phase with gaseous oxygen at a temperature between 15 and 200 C. (preferably 125 to 165 C.) under 50 to 500 (preferably 50 to 250) pounds per square inch pressure, continuing the oxidation until from 5% to 30% of the hydrocarbon has become oxidized. while separating from the oxidation mixture (e. g., azeotropically) the water produced by the oxidation reaction, withdrawing the reaction mixture from the oxidizer, distilling the resulting mixt'ure and purging therefrom an azeotropic distillate rich in benzene and lean in cyclohexane, or free of cyclohexane, recycling the main cyclohexane-contaming fraction (the benzene content of which has been lowered, or completely eliminated, as a result of the said distillation) back to the oxidizer, and recovering the portion of the reaction mixture which is less volatile than cyclohexane, said portion being rich in cyclohexanol and cyclohexanone. In general, the yield of cyclohexanol and cyclohexanone in this process on a large scale is virtually the same as the yield of cyclohexanol and cyclohexanone from pure cyclohexane, i. e., from 60% to 85% based upon the quantity of cyclohexane consumed, and the total yield of partial oxidation products which yield adipic acid upon further oxidation, lis substantially higher than the yield of cyclohexanol-cyclohexanone. In general, however, the chief'ingredients of the oxidation mixture after removal of the steamdlstillable hydrocarbon are cyclohexanol and cyclohexanone, e. g. the relative amounts of cyclohexanol and cyclohexanone, as compared with the amounts of other oxidized products corresponds to more than a 50% yield to cyclohexanol and cyclohexanone, in general. One of the chief advantages of the process of this invention over the previously known processes is that it makes possible the manufacture of cyclohexanol, cyclohexanone, and other valuable products from relatively cheap petroleum cycloheaxane crudes in a continuous manner without the accumulation of interferringsubstances, thus permitting continuous operation of the oxidizer for an unlimited i long period of time.

If desired, the process of this invention may be carried out in the absence of a catalyst. However, it has been found that somewhat higher yields of cyclohexanol and cyclohexanone are obtained if at least a small quantity of catalyst is employed. The quantity of catalyst may, indeed, be extremely minute, e. g. as little as 0.1 part per million of cobalt in the form of a hydrocarbon-soluble salt. Other catalysts which may be employed in place of cobalt (quantity, 0.1 to 1,000 parts per million, preferably about 0.5 to 50 parts per million) include hydrocarbon-soluble compounds of copper, cerium, vanadium, chromium, manganese, etc. The hydrocarbon-soluble compounds of cobalt. however. give the best results.

- The following table provides a comparison between the catalytic and the non-catalytic cyclohexane oxidation processes at various conversion levels.

TABLE Effect of cobalt naphthenate catalyst on yield of cyclohexanol and cycloheanone in the ozidation of cyclohexane with. air under preferred conditions (temperature, 125 to 165 C.; pressure, 50 to 250 pounds per square/inch) When the total conversion of hydrocarbon (i. e. percentage of hydrocarbon oxidized) is below yield comparisons are diflicult, vbut invariably the reaction product contains appreciable amounts of oxidation products having more than A one atom of oxygen combined per molecule of cyclohexane oxidized, whether or not acatalyst is employed; this is especially true at conversions higher than about 5%. From a practical standpoint it is not desirable to operate at conversions below 5% even though this results in very high yields of cyclohexanol and cyclohexanone. The best operating range, for many purposes, is about 12 to 15%, for in this range the yield is high, and the rate of production per unit volume of reaction space is optimum. Oxygen emciency is greatest at minimum conversion, but the relative value of the products land starting material is such that degree of oxidation to adipic acid intermediates, and their concentration in the converter eiliuent, are of greater importance than maximum yield of ketone and alcohol, etc., basedon hydrocarbon consumed. The amount of hydrocarbon recycled per unit of product is preferably kept as low as possible, and the quantity of useful oxidation products formed is preferably kept at an optimum.

The gaseous oxygen employed in the practice of the present invention may, if desired, be diluted with an inert gas such as nitrogen, CO2, etc. Air, or gaseous mixtures which are of relatively low oxygen content, may be used if desired.

Any petroleum cyclohexane crude may be employed in the practice of the invention. It is essential only that the hydrocarbon reactant contain a substantialquantity of cyclohexane. The expression petroleum cyclohexane crudef as employed herein, simply means a cyclohexane fraction derived from petroleum or petroleum products and containing a substantial quantity of other hydrocarbons from petroleum, which hydrocarbons distill with the cyclohexane fraction. It has been discovered, as stated above, that petroleum cyclohexane crudes normally contain small quantities of benzene, which it is not economical to remove by hydrogenation or otherwise. i The cyclohexane fractions employed in the practice of the invention may also contain numerous other hydrocarbons which are diiilcult or impossible to separate from cyclohexane by distillation, e. g. n-hexane, methyl cyclopentane, 2,2-dimethylpentane, 2,4-dimethyl pentane, etc. The latter two compounds are azeotropc with cyclohexane and benzene. In specific embodiments, as explained ,above, these hydrocarbons serve a useful purpose in the practice of the invention since they assist in the azeotropic separation of benzene from the recovered cyclohexane concentrate which has become enriched in benzene because of the loss of cyclohexane by oxidation. A suitable petroleum cyclohexane crude, which may -be employed in the practice of the invention, has a sulfur content in excess of 0.015% by weight, and contains, as substantially the only ingredients, from 1.5 to 3.0% by weight ctn-hexane, from 0.1 to 10% of benzene, from 2.0 to 18% of methyl cyclopentane, from 5.0 to 20% of dimethyl pentanes, 60 to 90% of cyclohexane and not more than about 1.5% of other hydrocarbon ingredients and sulfur compounds. With a crude of this composition the process of this invention has been operated continuously for a period of months on a large scale at a conversion of the hydrocarbon to total oxil dation products within the range of 10% to 15%,

without the accumulation of any interfering substances in the oxidation mixture. In the said operation, a cobalt naphthenate catalyst was employed and the yield of cyclohexanol-l-cyclohexanone was within the range of 60 to 75%, and the yield of products convertible to adipic acid was Y about to 85%.

The process of this invention may be carried out in any suitable equipment, e. g., tubular reactors, tower reactors, etc. Best results, however, are obtained when the oxidation vessel which is employed is a stirred autoclave, or when the process is operated in a continuous manner, a number of such stirredautoclaves in a series. If desired several such series can be connected in parallel; for example, there may be nine autoclaves arranged so that there are three trains, each containing three autoclaves. Each autoclave in the series should be equipped with a water-withdrawing means (condenser, with water draw-off) as stated above. The reaction mixture may be passed through the autoclaves continuously, the eiiluent from the first passing to the second, and so on. The eilluent from the last autoclave is, in preferred embodiments, conducted to a fractionating column for recovery of the unused hydrocarbon. This is accomplished either by direct fractionation or by steam distillation at a temperature up to 69 C., or somewhat higher, followed by separation of the benzene-containing azeotropic distillate by redistillation of the hydrocarbon layer. This azeotropic distillate boils for the most part at a. temperature very close to the boiling point of cyclohexane, just below 81 C., and entirely Within the range of 40 to 81 C. The main cyclohexane fraction, which of course contains a smaller percentage of benzene than the percentage of benzene in the oxidation mixture, is returned to the oxidation vessel. When water removal is accomplished by means of a condenser (generally operating at the pressure of lthe oxidizer) in the olf-gas line after each autoclave, the recovered hydrocarbon which is condensed along with the water should be separated in a decanter and piped to the oxidizer or to the main hydrocarbon recovery still. AThe final oil-gas is generally scrubbed with a high-boiling hydrocarbon or passed through a low temperature condenser for recovery of further amounts of benzene and, if desired, cyclohexane. A remarkable advantage in the yield of cyclohexanol and cyclohexanone (amounting to several per cent at a conversion of about is obtained if the recovered cyclohexane from the decanter and/or from the main hydrocarbon recovery still is returned to the first oxidizer, rather than to the second, or third, or subsequent oxidizer. The reason for this is that it results in a lower concentration of primary oxidation products in the first oxidizers, i. e. the average concentration along the train is lowered if the mixture is diluted with recycle hydrocarbon at the start of the train, rather than at the end thereof. All of the recovered cyclohexane is preferably returned to the first oxidizer for this reason.

While it is essential that the water which is produced by the oxidation reaction be removed from the oxidation mixture as fast as it is formed, it is nevertheless desirable to have Water present in the mixture after it has left the last oxidizer. The reason for this is that adipic acid, and other solid products, crystallize out when the oxidation mixture is cooled. Water is therefore preferably added to the oxidation mixture after it leaves the oxidizer but before the hydrocarbon recovery, to prevent precipitation of adipic acid. Also the presence of water is advantageous during the hydrocarbon recovery operations because it suppresses dehydration of cyclohexanol and cyclohexanone to such products as cyclohexylidene cyclohexanone, cyclohexyl ethers, and cyclohexyl esters.

The benzene-containing azeotropic distillate which is periodically or continuously purged from the oxidation mixture as above described, can be hydrogenated with Ni catalyst (e. g. in the manner described in U. S. 2,391,238) and returned to the oxidizers along with the main recovered cyclohexane fraction. A highly important discovery, which contributes in a very substantial way to the practical utility of the present invention, is the surprising observation that the oxidation reaction destroys the sulfur impurities which otherwise inhibit the hydrogenation of benzene in the petroleum cyclohexane crudes. These crudes quite invariably contain small amounts of organic sulfur compounds, and the present invention eliminates completely the very bothersome problem of removal of organic sulfur compounds which heretofore has rendered diillcult and expensive the elimination of traces of benzene in petroleum cyclohexane crudes. The sulfur content of the recovered benzene fractions is generally below 0.001%, and the sulfur content of the original cyclohexane crude is commonly in excess of 0.015%.

The accompanying diagrammatic drawing illustrates one method for practicing the invention. Air is passed through a preheater I and is injected into the oxidizers 2, 3, and 4. The hydrocarbon feed containing the dissolved catalyst is also injected into the oxidizer. This hydrocarbon feed may contain a small percentage (0.1 to 2.0% by weight) of an initiator such as an organic peroxy compound, ketone (preferably cyclohexanone), aldehyde, etc., but this is not essential once the reaction is underway. The liquid efiiuent is withdrawn from each oxidizer in series through the draw-ofi lines 5, 6, and l. The emuent from the last oxidizer in the train is mixed with water, passed through a cooler and discharge tank 8. From the latter it is piped to a steam distillation apparatus 9 from which the hydrocarbon distillate is discharged overhead, and the less volatile oxidation products are withdrawn as residue. The hydrocarbon distillate is then washedwith water or aqueous alkali in the l washing device Il. after which it is conducted to the still I I which separates out the benzene azeotrope. The remaining hydrocarbon is piped through the conduit I2 to the hydrocarbon feed line il. The oil-gas from the rst oxidizer 2 is cooled in the condenser i4 which produces a condensate of water and hydrocarbon. The condensate is conducted through the pipe I5 to a decanter it from which the water layer is continuously withdrawn and sewered. The hydrocarbon layer from the decanter It is conducted back to autoclave 2. Each of the other autoclaves 3' and I in the train is equipped with a condenser l1, i8, and decanter II, 2l, by means of which water is separated from the oxidation mixture, the hydrocarbon layer from each decanter being conducted to the autoclave from which the said hydrocarbon had been vaporized, or to the first autoclave 2.

By carrying out the oxidation process as described above, the oxidation mixture is kept virtually free of water. Unless a means is provided for removal of water from the oxidizers, the concentration of water dispersed in the reaction mixture increases as the oxidation progresses until it becomes suiliciently high to inhibit the oxidation. 'I'he shutdowns caused by the occurrence of this phenomenon are completely avoided by employing the water withdrawing means described above.

The invention is illustrated further by means of the following examples.

Example 1.-Into a stirred autoclave having a capacity of 1 gallon is placed 2500 cc. of a petrotrimm concentrate having the following composi- High boilers, and organic sulfur compounds including those boiling in benzene range- 1.1

lMixture of 22-dimethyl pentane B. P.:79.2 and 2,4-dimeu1y1 nime (n. P.=so.5).( Boiling pelin or cyclohexane il 80.7

Cobalt naphthenate (equivalent to 50 P. P. M. of cobalt based upon the total weight of the petroleum concentrate )and cyclohexanone (0.3% by weight) are then introduced and the resulting mixture is oxidized with air which is passed into the mixture at the rate of volumes (S. T. P.) of air per unit volume of reaction space per hour under a pressure of 100 pounds per square inch (gauge) at a temperature of C. The oxidation is continued for a period of 60 minutes, at the end of which time 14.3% of the hydrocarbon has been converted to oxidation products. 'I'he unused hydrocarbon, which is recovered by steam distillation as explained below, is reoxidized with make-up hydrocarbon suiiicient in amount to make a charge of 2500 cc. During the oxidation a portion of the hydrocarbon is continuously vaporized and condensed. The condensate, before returning to the oxidation mixture. is permitted to separate into two layers, and the bottom layer which consists essentially of water. is continuously withdrawn. In this manner the water which is produced by the oxidation reaction is removed from the reaction mixture as rapidly as it is formed. After the oxidation is completed, the liquid product is admixed with water. and con- 9 ducted to the hydrocarbon recovery system. The hydrocarbon recovery system includes a 25 plate column. All of the recovered hydrocarbon is returned to the oxidation vessel. The remainder of the product, i. e. the ingredients of the oxidation mixture which have .a boiling point higher than the boiling point of cyclohexane, are withdrawn and recovered separately. After prolonged operation in this manner. the benzene content of the recovered cyclohexane has increased to 4.8%. In order to remove benzene from the recovered cyclohexane. it is passed through a 45 plate fractionating column operated at a reflux ratio of 47:'1. This permits withdrawal of an azeotropic distillate from the top of the column, which azeotropic distillate contains 20.7% cyclohexane and 41.5% benzene. This distillate is found to be sulfur-free. At a somewhat lower reux ratio (26:1) the azeotropic distillate withdrawn from the top of the column when the feed composition contained 5.4% benzene has a cyclohexane content of 35.2% and a benzene content of 36.3%. The sulfur-free benzene-containing azeotropic distillate is hydrogenated in the known manner using a nickel-aluminum alloy catalyst until substantially all of the benzene has been converted to cyclohexane. 'Ihe resulting hydrogenation product is also recirculated to the oxidation vessel. Operation is continued in this manner for a prolonged period of time, the yield of cycloaction of concentrated nitric acid. The chief products. however. are cyclohexanol+cyclohexa none (in about equal amounts). which are obtained in yields of about 55% based upon the amount of cyclohexane consumed.

It is to be understood that the above examples are illustrative only and that many ways of practicing the invention will occur to those who are hexanol and cyclohexanone being about 60% to 70% of the theoretical, based on the amount of cyclohexane consumed.

Example 2.--Example 1 is repeated using a petroleum concentrate having the following composition.

. Vol. per cent n-Hexane 2.2 Benzene 0.6 Methyl cyclopentane 15.5 Isoheptanes 12.3 Cyclohexane 68.8 High boilers, sulfur compounds. etc 0.6

After 8 cycles the recovered hydrocarbon contains 68.8% by volume of cyclohexane. -A composite of theoxidation products thus obtained is exhaus- `tively steam distilled, and the steam-distilled oil is fractionated under vacuum. The portion boiling in the 74 to 76 C /50 mm. range contains 95.1% cyclohexanone and the portion boiling in the 89 to 91 C./10 mm. range contains 94.5% cyclohexanol. The yield of cyclohexanol and cyclohexanone is about 60% to 70%, based on the cyclohexane consumed.

Example 3.-Example 1 is repeated using a petroleum concentrate containing 85% cyclohexane and 4.4% benzene. the remainder of the hydrocarbon mixture being methyl cyclopentane and isoheptanes. The oxidation product contains, in addition to cyclohexanol and cyclohexanone, appreciable amounts of monobasic acids such as acetic and formic acids; ketones, including acetone, hexanone-2, methylethyl ketone, and mesityl oxide; and alcohols, including methanol, ethanol, propanols and n-butanols. Thepetroleum concentrate initially contains 60 P. P. M. sulfur but the recovered hydrocarbon contains only 5.1 P. P. M. sulfur. The non-volatile oxidation products, i. e. the products which do not distill with steam, contain adipate esters, deltaformyl valerie acid, epsilon-hydroxy caproic acid and its esters, along with other products which give adipic acid when subjected to the oxidizing skilled in the art. For example, the process can be operated in an intermittent or batchwise manner. but, of course, the advantages of iie invention, including the advantage which results from permitting the benzene concentration to build up to a sulciently high concentration to permit withdrawal thereof from the oxidized mixture economically by azeotropic distillation, are of `the greatest value when the process is operated continuously.

Valuable products other than ing adipic acid on further oxidation are obtained in the practice of the invention. These other products include compounds (dibasic acids, esters, etc.) which, when hydrogenated, yield a series of polymethylene glycols which are of outstanding utility in the manufacture of glycol ester plasticizers.

Since many different embodiments of the. invention will occur to those who are skilled in the art, it will be understood that we do not limit ourselves except as set forth' in the following claims.

We claim:

1. A process for manufacturing partial oxidation products of cyclohexane, including cyclohexanol and cyclohexanone, `which comprises reacting a. petroleum cyclohexane crude, said crude containing at least 0.1% of benzene, in the liquid phase with gaseous oxygen at a temperature of to 200 C. under a pressure of 50 to 500 pounds per square inch in the presence of a catalytic quantity of a hydrocarbon-soluble compound of cobalt, said petroleum cyclohexane crude having initially a sufiicientlyhigh content of organic sulfur compounds to poison a nickelhydrogenation catalyst when an attempt is made to convert the benzene in the said crude to cyclohexane by hydrogenation of the crude in the presence of the said catalyst, continuing the oxidation while separating water from the oxidation mixture substantially as rapidly as the said water is formed by the oxidation reaction, until from 5% to. 30% of the hydrocarbon in the petroleum cyclohexane crude has become oxidized, admixing water with the resulting oxidation mixture, distilling the resulting mixtureand thereby separating therefrom an azeotropic distillate containing benzene and cyclohexane, said distillate having a suiliciently low content of organic sulfur compounds that the benzene contained therein can be readily converted y to cyclohexane by hydrogenation of the azeotropic "distillate in the presence of a nickel catalyst.

continuing the said distillation and thereby sepa.- rating also a cyclohexane fraction having a smaller benzene:cyclohexane ratio than the benzene:cyclohexane ratio in the said oxidation mixture immediately prior to the said distillation, recycling the said cyclohexane fraction back to the oxidizer, hydrogenating the said azeotropic distillate and returning the resulting hydrogenation product to the oxidizer, recovering the portion of the oxidation mixture which is less volatile than cyclohexane, said portion being rich in cyclohexanol and cyclohexanone, and continuing the said oxidation in the presence of a catalytic products yieldll quantity of a hydrocarbon-soluble compound of cobalt, with make-up petroleum cyclohexane crude.

2. The process of claim 1 in which the catalyst is cobalt naphthenate.

3. The process of claim 1 in which the hydrocarbon charged into the oxidizer contains from 0.1 to 10.0% by weight of benzene.

4. The process of claim 1 in which the hydrocarbon charged into the oxidizer contains from 0.1 to 10.0% by weight of benzene and from 5.0 to 20.0% by weight of dimethyl pentanes.

5. The process ot claim 1, performed in a con- I -tinuous manner, the oxidation mixture being continuously withdrawn from the oxidizer and l5 2,439,513

l2 distilled, and the cyclohexane traction being continuously returned to the oxidir.

CLEMENT H. HAMBLET. FRANKLIN S. CHANCE.A

REFERENCES cl'rlazn- .The followingA references are ot record in the ille of this patent:

UNITED STATES PATENTS Number NarneV Date 2,223,494 Loder Dec. 3, 1940 `2,288,769 Aneman et a1. July' '1, 1942 2,410,642 Farkas etal Nov. 5, 1946 Hamblet et al Apr. 13, 1948 

1. A PROCESS FOR MANUFACTURING PARTIAL OXIDATION PRODUCTS OF CYCLOHEXANE, INCLUDING CYCLOHEXANOL AND CYCLOHEXANONE, WHICH COMPRISES REACTING A PETROLEUM CYCLOHEXANE CRUDE, SAID CRUDE CONTAINING AT LEAST 0.1% OF BENZENE, IN THE LIQUID PHASE WITH GASEOUS OXYGEN AT A TEMPERATURE OF 75* TO 200* C. UNDER A PRESSURE OF 50 TO 500 POUNDS PER SQUARE INCH IN THE PRESENCE OF A CATALYTIC QUANTITY OF A HYDROCARBON-SOLUBLE COMPOUND OF COBALT, SAID PETROLEUM CYCLOHEXANE CRUDE HAVING INITIALLY A SUFFICIENTLY HIGH CONTENT OF ORGANIC SULFUR COMPOUNDS TO POISON A NICKEL HYDROGENATION CATALYST WHEN AN ATTEMPT IS MADE TO CONVERT THE BENZENE IN THE SAID CRUDE TO CYCLOHEXANE BY HYDROGENATION OF THE CRUDE IN THE PRESENCE OF THE SAID CATALYST, CONTINUING THE OXIDATION WHILE SEPARATING WATER FROM THE OXIDATION MIXTURE SUBSTANTIALLY AS RAPIDALY AS THE SAID WATER IS FORMED BY THE OXIDATION REACTION, UNTIL FROM 5% TO 30% OF THE HYDROCARBON IN THE PETROLEUM CYCLOHEXANE CRUDE HAS BECOME OXIDIZED, ADMIXING WATER WITH THE RESULTING OXIDATION MIXTURE, DISTILLING THE RESULTING MIXTURE AND THEREBY SEPARATING THEREFROM AN AZEOTROPIC DISTILLATE CONTAINING BENZENE AND CYCLOHEXANE, SAID DISTILLATE HAVING A SUFFICIENTLY LOW CONTENT OF ORGANIC SULFUR COMPOUNDS THAT THE BENZENE CONTAINED THEREIN CAN BE READILY CONVERTED TO CYCLOHEXANE BY HYDROGENATION OF THE AZETROPIC DISTILLATE IN THE PRESENCE OF A NICKEL CATALYST, CONTINUING THE SAID DISTILLATION AND THEREBY SEPARATING ALSO A CYCLOHEXANE FRACTION HAVING A SMALLER BENZENE:CYCLOHEXANE RATIO THAN THE BENZENE:CYCLOHEXANE RATIO IN THE SAID OXIDATION MIXTURE IMMEDIATELY PRIOR TO THE SAID DISTILLATION, RECYCLING THE SAID CYCLOHEXANE FRACTION BACK TO THE OXIDIZER, HYDROGENATING THE SAID AZETROPIC DISTILLATE AND RETURNING THE RESULTING HYDROGENATION PRODUCT TO THE OXIDIZER, RECOVERING THE PORTION OF THE OXIDATION MIXTURE WHICH IS LESS VOLATILE THAN CYCLOHEXANE, SAID PORTION BEING RICH IN CYCLOHEXANOL AND CYCLOHEXANONE, AND CONTINUING THE SAID OXIDATION IN THE PRESENCE OF A CATALYTIC QUANTITY OF A HYDROCARBON-SOLUBLE COMPOUND OF COBALT, WITH MAKE-UP PETROLEUM CYCLOHEXANE CRUDE. 